This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. There is a growing interest in the use of biodiesel to replace petroleum diesel fuel as biodiesel has been suggested to pose less risk to human health and the environment. Multiple tailpipe emissions studies have determined use of biodiesel blends reduces emissions of carbon monoxide, particulate matter, and hydrocarbons compared to traditional petroleum diesel. However, it is less clear whether reduction of tailpipe emissions will translate into reduced occupational and environmental exposures, or reduced health risk. The emissions data and perceived political benefits of reducing foreign oil imports have motivated organizations to switch to biodiesel blends. Total 2008 U.S. biodiesel production volume is expected to be between 500 and 600 million gallons (McCormick 2008). This increase in production has occurred despite a paucity of exposure and human health effects research (Swanson et al. 2007). Recent research in our laboratory demonstrated 20% biodiesel/80% petroleum diesel (B20) use reduced airborne fine particulate matter (PM2.5) exposure concentrations by approximately 60%. Conversely, B20 use demonstrated a 370% increase in organic carbon concentrations. However, the chemical nature of these organics has not yet been characterized. This project characterizes diesel/biodiesel occupational and environmental exposure profiles in a non-road application, with a focus on fine and ultra fine particulate matter. Measurement of 'real world'exposures provides valuable data to evaluate potential health risks to workers and the local public, and is often a weak link in the risk assessment process. We will specifically investigate the hypothesis that controlling the blend percentage of biodiesel (B20 [unreadable]B50) will result in significant reductions in total PM2.5 mass;significant differences in PM2.5 morphology;and significant decreases in highly toxic organic carbon species (PAH's &n-PAH's).